Charged particle beam apparatuses have many functions in a plurality of industrial fields, including, but not limited to, inspection of semiconductor devices during manufacturing, exposure systems for lithography, detecting devices and testing systems. Thus, there is a high demand for structuring and inspecting specimens within the micrometer and nanometer scale.
Micrometer and nanometer scale process control, inspection or structuring is often done with charged particle beams, e.g., electron beams, which are generated and focused in charged particle beam devices, such as electron microscopes or electron beam pattern generators. Charged particle beams offer superior spatial resolution compared to, e.g., photon beams, due to their short wavelengths.
For charged particle beam systems such as a scanning electron microscope (SEM) the brightness of the electron gun is becoming increasingly important. Thereby, the virtual size of the source, i.e., the size of the portion of the emitter tip that is imaged, can be used to improve the brightness of the charged particle source. However, this may result in an increasingly complex alignment of the charged particle beam with respect to the optical axis. Thus, there is a need for an improved alignment of a charged particle beam to an optical axis, particularly for high brightness charged particle sources.